Methods for coupling conduits to each other by providing them with a large flexibility have been proposed so far and they are practically used. To secure the flexibility, it is advantageous to use a spherical portion so as to obtain a relatively large flexibility. That is, tubes having ends on which hollow spherical portions are formed so as to be fitted to each other inside and outside are used. The hollow spherical portions are fitted and coupled to each other, a holding portion body is provided to the outside spherical portion, and the inside spherical portion is rotatably held between the outside spherical portion and the holding portion body.
Moreover, by using a set of above flexible joints and slidably coupling the tubes at the joints to each other, an extensible portion between tubes is formed between the above described flexible portions on both sides to obtain not only flexibility but also extensibility. In this case, it is possible to provide flexibility and extensibility to conduits connected to both ends of the joint mechanism while they are parallel.
The above conventional flexible joint and flexible extensible joint have an advantage that a large flexibility and extensibility are obtained. However, because these joints flexibly extend or contract while securing an accurate sealing condition by a sealing material between the above flexible portion and extensible portion, the accuracy of the sealing condition is proportional to the tightness of the sealing material and a considerable frictional resistance is inevitably produced when the joint actually flexibly extends or contracts. Therefore there is a disadvantage that actual flexible extension or contraction is not smoothly performed due to the frictional resistance of the sealing material.
In the case of the conventional joints described above, it is essential to securely and tightly seal the sealing material in order to tightly couple those portion bodies. Therefore, such coupling cannot be sufficiently obtained or leakage may occur when the coupling is inaccurate. Moreover, the sufficiently tightened sealing material has a disadvantage that it is aged or deformed and adequate durability is hardly obtained.
When the above extensible flexible joint is used as a bent tube, the joint is extended due to the pressure of the fluid circulating through the tube. Moreover, when the joint is led from a fixed portion 28 and connected so as to form a bent conduit 26 as shown in FIG. 7, an unnecessary bending force is produced in a conduit portion body 27 as shown by imaginary lines and a deformed portion 27 is formed on the conduit or the conduit is cracked or broken.